Phosphorylation of Leukotriene C4 Synthase at Serine 36 Impairs Catalytic Activity

Structure Bioinformatics of Six Human Integral Transmembrane Enzymes and their AlphaFold3 Predicted Water-Soluble QTY Analogs: Insights into FACE1 and STEA4 Binding Mechanisms

OBJECTIVE

Human integral membrane enzymes are essential for catalyzing a wide range of biochemical reactions and regulating key cellular processes. However, studying these enzymes remains challenging due to their hydrophobic nature, which necessitates the use of detergents. This study explores whether applying the QTY code can reduce the hydrophobicity of these enzymes while preserving their structures and functions, thus facilitating bioinformatics analysis of six key integral membrane enzymes: MGST2, LTC4S, PTGES, FACE1, STEA4, and SCD.

METHODS

The water-soluble QTY analogs of the six membrane enzymes were predicted using AlphaFold3. The predicted structures were superposed with CyroEM determined native structures in PyMOL to observe changes in structure and protein-ligand binding ability.

RESULTS

The native membrane enzymes superposed well with their respective QTY analogs, with the root mean square deviation (RMSD) ranging from 0.273 Å to 0.875 Å. Surface hydrophobic patches on the QTY analogs were significantly reduced. Importantly, the protein-ligand interactions in FACE1 and STEA4 were largely preserved, indicating maintained functionality.

CONCLUSION

Our structural bioinformatics studies using the QTY code and AlphaFold3 not only provide the opportunities of designing more water-soluble integral membrane enzymes, but also use these water-soluble QTY analogs as antigens for therapeutic monoclonal antibody discovery to specifically target the key integral membrane enzymes.

A helminth enzyme subverts macrophage-mediated immunity by epigenetic targeting of prostaglandin synthesis

The molecular mechanisms by which worm parasites evade host immunity are incompletely understood. In a mouse model of intestinal helminth infection using Heligmosomoides polygyrus bakeri (Hpb), we show that helminthic glutamate dehydrogenase (heGDH) drives parasite chronicity by suppressing macrophage-mediated host defense. Combining RNA-seq, ChIP-seq, and targeted lipidomics, we identify prostaglandin E2 (PGE2) as a major immune regulatory mechanism of heGDH. The induction of PGE2 and other immunoregulatory factors, including IL-12 family cytokines and indoleamine 2,3-dioxygenase 1, by heGDH required p300-mediated histone acetylation, whereas the enzyme's catalytic activity suppressed the synthesis of type 2-promoting leukotrienes by macrophages via 2-hydroxyglutarate. By contrast, the induction of immunoregulatory factors involved the heGDH N terminus by potentially mediating interactions with cellular targets (CD64 and GPNMB) identified by proteomics. Type 2 cytokines counteracted suppressive effects of heGDH on host defense, indicating that type 2 immunity can limit helminth-driven immune evasion. Thus, helminths harness a ubiquitous metabolic enzyme to epigenetically target type 2 macrophage activation and establish chronicity.

Correlation between LTC4S -444 A>C polymorphism and susceptibility to asthma: A meta-analysis and trial sequential analysis

Background

This study aims to uncover the potential correlation between LTC4S -444 A>C polymorphism and susceptibility to asthma.

Methods

Literatures reporting the correlation between LTC4S -444 A>C polymorphism and susceptibility to asthma published before 1st June, 2019 were searched in PubMed, Embase, Cochrane, Wanfang and CNKI. Eligible literatures were enrolled and their data were extracted. OR and its 95% CI were calculated for assessing the correlation between LTC4S -444 A>C polymorphism and susceptibility to asthma. The included data were weighted by an inverse variance and then analyzed by a fixed or random effects model. Heterogeneity test and sensitivity analysis were performed on the enrolled reports. STATA12.1 and TSA (trial sequential analysis) were utilized for analyses.

Three-dimensional growth reveals fine-tuning of 5-lipoxygenase by proliferative pathways in cancer

The leukotriene (LT) pathway is positively correlated with the progression of solid malignancies, but the factors that control the expression of 5-lipoxygenase (5-LO), the central enzyme in LT biosynthesis, in tumors are poorly understood. Here, we report that 5-LO along with other members of the LT pathway is up-regulated in multicellular colon tumor spheroids. This up-regulation was inversely correlated with cell proliferation and activation of PI3K/mTORC-2- and MEK-1/ERK-dependent pathways. Furthermore, we found that E2F1 and its target gene MYBL2 were involved in the repression of 5-LO during cell proliferation. Importantly, we found that this PI3K/mTORC-2- and MEK-1/ERK-dependent suppression of 5-LO is also existent in tumor cells from other origins, suggesting that this mechanism is widely applicable to other tumor entities. Our data show that tumor cells fine-tune 5-LO and LT biosynthesis in response to environmental changes repressing the enzyme during proliferation while making use of the enzyme under cell stress conditions, implying that tumor-derived 5-LO plays a role in the manipulation of the tumor stroma to quickly restore cell proliferation.

Exploring human CYP4 enzymes: Physiological roles, function in diseases and focus on inhibitors

The cytochrome P450 (CYP)4 family of enzymes are monooxygenases responsible for the ω-oxidation of endogenous fatty acids and eicosanoids and play a crucial part in regulating numerous eicosanoid signaling pathways. Recently, CYP4 gained attention as a potential therapeutic target for several human diseases, including cancer, cardiovascular diseases and inflammation. Small-molecule inhibitors of CYP4 could provide promising treatments for these diseases. The aim of the present review is to highlight the advances in the field of CYP4, discussing the physiology and pathology of the CYP4 family and compiling CYP4 inhibitors into groups based on their chemical classes to provide clues for the future discovery of drug candidates targeting CYP4.

Structures of Leukotriene Biosynthetic Enzymes and Development of New Therapeutics

Leukotrienes are potent immune-regulating lipid mediators with patho-genic roles in inflammatory and allergic diseases, particularly asthma. These autacoids also contribute to low-grade inflammation, a hallmark of cardiovascular, neurodegenerative, metabolic, and tumor diseases. Biosynthesis of leukotrienes involves release and oxidative metabolism of arachidonic acid and proceeds via a set of cytosolic and integral membrane enzymes that are typically expressed by cells of the innate immune system. In activated cells, these enzymes traffic and assemble at the endoplasmic and perinuclear membrane, together comprising a biosynthetic complex. Here we describe recent advances in our molecular understanding of the protein components of the leukotriene-synthesizing enzyme machinery and also briefly touch upon the leukotriene receptors. Moreover, we discuss emerging opportunities for pharmacological intervention and development of new therapeutics.

Integral Membrane Enzymes in Eicosanoid Metabolism: Structures, Mechanisms and Inhibitor Design

Eicosanoids are potent lipid mediators involved in central physiological processes such as hemostasis, renal function and parturition. When formed in excess, eicosanoids become critical players in a range of pathological conditions, in particular pain, fever, arthritis, asthma, cardiovascular disease and cancer. Eicosanoids are generated via oxidative metabolism of arachidonic acid along the cyclooxygenase (COX) and lipoxygenase (LOX) pathways. Specific lipid species are formed downstream of COX and LOX by specialized synthases, some of which reside on the nuclear and endoplasmic reticulum, including mPGES-1, FLAP, LTC4 synthase, and MGST2. These integral membrane proteins are members of the family "membrane-associated proteins in eicosanoid and glutathione metabolism" (MAPEG). Here we focus on this enzyme family, which encompasses six human members typically catalyzing glutathione dependent transformations of lipophilic substrates. Enzymes of this family have evolved to combat the topographical challenge and unfavorable energetics of bringing together two chemically different substrates, from cytosol and lipid bilayer, for catalysis within a membrane environment. Thus, structural understanding of these enzymes are of utmost importance to unravel their molecular mechanisms, mode of substrate entry and product release, in order to facilitate novel drug design against severe human diseases.

Arachidonic acid promotes the binding of 5-lipoxygenase on nanodiscs containing 5-lipoxygenase activating protein in the absence of calcium-ions

Among the first steps in inflammation is the conversion of arachidonic acid (AA) stored in the cell membranes into leukotrienes. This occurs mainly in leukocytes and depends on the interaction of two proteins: 5-lipoxygenase (5LO), stored away from the nuclear membranes until use and 5-lipoxygenase activating protein (FLAP), a transmembrane, homotrimeric protein, constitutively present in nuclear membrane. We could earlier visualize the binding of 5LO to nanodiscs in the presence of Ca²⁺-ions by the use of transmission electron microscopy (TEM) on samples negatively stained by sodium phosphotungstate. In the absence of Ca²⁺-ions 5LO did not bind to the membrane. In the present communication, FLAP reconstituted in the nanodiscs which could be purified if the His-tag was located on the FLAP C-terminus but not the N-terminus. Our aim was to find out if 1) 5LO would bind in a Ca²⁺-dependent manner also when FLAP is present? 2) Would the substrate (AA) have effects on 5LO binding to FLAP-nanodiscs? TEM was used to assess the complex formation between 5LO and FLAP-nanodiscs along with, sucrose gradient purification, gel-electrophoresis and mass spectrometry. It was found that presence of AA by itself induces complex formation in the absence of added calcium. This finding corroborates that AA is necessary for the complex formation and that a Ca²⁺-flush is mainly needed for the recruitment of 5LO to the membrane. Our results also showed that the addition of Ca²⁺-ions promoted binding of 5LO on the FLAP-nanodiscs as was also the case for nanodiscs without FLAP incorporated. In the absence of added substances no 5LO-FLAP complex was formed. Another finding is that the formation of a 5LO-FLAP complex appears to induce fragmentation of 5LO in vitro.

Activation of metabolite receptor GPR91 promotes platelet aggregation and transcellular biosynthesis of leukotriene C4

BACKGROUND

Succinate is a Krebs cycle intermediate whose formation is enhanced under metabolic stress, and for which a selective sensor GPR91 has been identified on various cell types including platelets. Platelet-derived eicosanoids play pivotal roles in platelet activation/aggregation, which is key to thrombus formation and progression of atherothrombosis.

OBJECTIVES

This study aims to decipher the molecular mechanism(s) and potential involvement of eicosanoids in succinate enhanced platelet activation/aggregation.

METHODS

We used liquid chromatography-mass spectrometry (LC-MS)/MS-based lipid mediator profiling to identify eicosanoids regulated by succinate. We ran light transmittance aggregometry and flow cytometry to assess platelet aggregation, P-selectin expression, and platelet-polymorphonuclear leukocyte (PMN) adherence. Various pharmacological tools were used to assess the contributions of GPR91 signalling and eicosanoids in platelet aggregation.

RESULTS

Succinate and two types of synthetic non-metabolite GPR91 agonists-cis-epoxysuccinate (cES) and Cmpd131-potentiated platelet aggregation, which was partially blocked by a selective GPR91 antagonist XT1. GPR91 activation increased production of 12-hydroxy-eicosatetraenoic acid (12-HETE), thromboxane (TX) A2 , and 12-hydroxy-heptadecatrienoic acid (12-HHT) in human platelets, associated with phosphorylation of cytosolic phospholipase A2 (cPLA2 ), suggesting increased availability of free arachidonic acid. Blocking 12-HETE and TXA2 synthesis, or antagonism of the TXA2 receptor, significantly reduced platelet aggregation enhanced by GPR91 signalling. Moreover, platelet-PMN suspensions challenged with succinate exhibited enhanced transcellular biosynthesis of leukotriene C4 (LTC4 ), a powerful proinflammatory vascular spasmogen.

CONCLUSION

Succinate signals through GPR91 to promote biosynthesis of eicosanoids, which contribute to platelet aggregation/activation and potentially vascular inflammation. Hence, GPR91 may be a suitable target for pharmacological intervention in atherothrombotic conditions.

Leukotriene biosynthetic enzymes as therapeutic targets

Leukotrienes are powerful immune-regulating lipid mediators with established pathogenic roles in inflammatory allergic diseases of the respiratory tract - in particular, asthma and hay fever. More recent work indicates that these lipids also contribute to low-grade inflammation, a hallmark of cardiovascular, neurodegenerative, and metabolic diseases as well as cancer. Biosynthesis of leukotrienes involves oxidative metabolism of arachidonic acid and proceeds via a set of soluble and membrane enzymes that are primarily expressed by cells of myeloid origin. In activated immune cells, these enzymes assemble at the endoplasmic and perinuclear membrane, constituting a biosynthetic complex. This Review describes recent advances in our understanding of the components of the leukotriene-synthesizing enzyme machinery, emerging opportunities for pharmacological intervention, and the development of new medicines exploiting both antiinflammatory and pro-resolving mechanisms.

Immune-regulation and -functions of eicosanoid lipid mediators

Bioactive lipids regulate most physiological processes, from digestion to blood flow and from hemostasis to labor. Lipid mediators are also involved in multiple pathologies including cancer, autoimmunity or asthma. The pathological roles of lipid mediators are based on their intricate involvement in the immune system, which comprises source and target cells of these mediators. Based on their biosynthetic origin, bioactive lipids can be grouped into different classes [e.g. sphingolipids, formed from sphingosine or eicosanoids, formed from arachidonic acid (AA)]. Owing to the complexity of different mediator classes and the prominent immunological roles of eicosanoids, this review will focus solely on the immune-regulation of eicosanoids. Eicosanoids do not only control key immune responses (e.g. chemotaxis, antigen presentation, phagocytosis), but they are also subject to reciprocal control by the immune system. Particularly, key immunoregulatory cytokines such as IL-4 and IFN-γ shape the cellular eicosanoid profile, thus providing efficient feedback regulation between cytokine and eicosanoid networks. For the purpose of this review, I will first provide a short overview of the most important immunological functions of eicosanoids with a focus on prostaglandins (PGs) and leukotrienes (LTs). Second, I will summarize the current knowledge on immunological factors that regulate eicosanoid production during infection and inflammation.

Leukotriene B₄ Metabolism and p70S6 Kinase 1 Inhibitors: PF-4708671 but Not LY2584702 Inhibits CYP4F3A and the ω-Oxidation of Leukotriene B₄ In Vitro and In Cellulo

LTB4 is an inflammatory lipid mediator mainly biosynthesized by leukocytes. Since its implication in inflammatory diseases is well recognized, many tools to regulate its biosynthesis have been developed and showed promising results in vitro and in vivo, but mixed results in clinical trials. Recently, the mTOR pathway component p70S6 kinase 1 (p70S6K1) has been linked to LTC4 synthase and the biosynthesis of cysteinyl-leukotrienes. In this respect, we investigated if p70S6K1 could also play a role in LTB4 biosynthesis. We thus evaluated the impact of the p70S6K1 inhibitors PF-4708671 and LY2584702 on LTB4 biosynthesis in human neutrophils. At a concentration of 10 μM, both compounds inhibited S6 phosphorylation, although neither one inhibited the thapsigargin-induced LTB4 biosynthesis, as assessed by the sum of LTB4, 20-OH-LTB4, and 20-COOH-LTB4. However, PF-4708671, but not LY2584702, inhibited the ω-oxidation of LTB4 into 20-OH-LTB4 by intact neutrophils and by recombinant CYP4F3A, leading to increased LTB4 levels. This was true for both endogenously biosynthesized and exogenously added LTB4. In contrast to that of 17-octadecynoic acid, the inhibitory effect of PF-4708671 was easily removed by washing the neutrophils, indicating that PF-4708671 was a reversible CYP4F3A inhibitor. At optimal concentration, PF-4708671 increased the half-life of LTB4 in our neutrophil suspensions by 7.5 fold, compared to 5 fold for 17-octadecynoic acid. Finally, Michaelis-Menten and Lineweaver-Burk plots indicate that PF-4708671 is a mixed inhibitor of CYP4F3A. In conclusion, we show that PF-4708671 inhibits CYP4F3A and prevents the ω-oxidation of LTB4 in cellulo, which might result in increased LTB4 levels in vivo.